The development of fusion power has been an area of massive investment of time and money for many years. This investment has been largely centred on developing a large scale fusion reactor, at great cost. However, there are other theories that predict much simpler and cheaper mechanisms for creating fusion. Of interest here is the umbrella concept “inertial confinement fusion”, which uses mechanical forces (such as shock waves) to concentrate and focus energy into very small areas.
Much of the confidence in the potential in alternative methods of inertial confinement fusion comes from observations of a phenomenon called sonoluminescence. This occurs when a liquid containing appropriately sized bubbles is driven with a particular frequency of ultrasound. The pressure wave causes bubbles to expand and then collapse very violently; a process usually referred to as inertial cavitation. The rapid collapse of the bubble leads to non-equilibrium compression that causes the contents to heat up to an extent that they emit light [Gaitan, D. F., Crum, L. A., Church, C. C., and Roy, R. A., Journal of the Acoustical Society of America, 91(6), 3166-3183 June (1992)]. There have been various efforts to intensify this process and one group has claimed to observe fusion [Taleyarkhan, R. P., West, C. D., Cho, J. S., Lahey, R. T., Nigmatulin, R. I., and Block, R. C., Science, 295(5561), 1868-1873 March (2002)]. However, the observed results have not yet been validated or replicated, in spite substantial effort [Shapira, D. and Saltmarsh, M., Physical Review Letters, 89(10), 104302 September (2002)]. This is not the only proposed mechanism that has led to luminescence from a collapsing bubble; however it is the most documented.
Luminescence has also been observed from a bubble collapsed by a strong shock wave [Bourne, N. K. and Field, J. E., Philosophical Transactions of the Royal Society of London Series A-Mathematical Physical and Engineering Sciences, 357(1751), 295-311 February (1999)]. It has been proposed in U.S. Pat. No. 7,445,319 to fire spherical drops of water moving at very high speed (˜1 km/s) into a rigid target to generate an intense shockwave. This shockwave can be used to collapse bubbles inside the droplet. Another mechanism of using a shockwave to collapse a bubble is described in WO 2011/138622, where the present Applicants have proposed to collapse a bubble within a liquid by applying a high pressure shockwave to the liquid. Although this affords a number of advantages over previous techniques, e.g. not requiring high speed droplet impact, the apparatus needed to generate high enough pressure shockwaves can be complicated and expensive.